The present invention is generally related to electronic components and, more particularly, is related to reflowing of solder joints of such electronic components.
In many applications requiring high-precision alignment of fiber optic components, it is desired to attach the optical component onto a substrate using solder, while maintaining the alignment of the optical component with its desired target. If two or more components share the same substrate, it is sometimes not possible to globally heat the substrate to melt the solder while maintaining alignment of each component on the substrate. When the substrate is globally heated, other solder joints may reflow, causing misalignment of the optical components.
Often, each component is sequentially aligned while locally heating each solder joint. One method of local heating involves the use of a contacting heat source, for example a soldering iron tip, in order to reflow the solder. There are several disadvantages associated with this method of reflow. For example, the solder joint is typically very small and it is a challenge to create a solder tip in such a small size. It is also difficult to accurately place the tip of the iron. Further, if high-temperature solder is used, the solder tip can degrade very quickly, adding time and cost to the process because of the high cost and incidence of replacement of the solder tips. Additionally, manipulating the small solder tip onto the solder joint is a slow and tedious process. Further, because the solder iron tip must actually touch the solder, the solder iron tip can potentially disturb alignment of the optical component during the reflow process.
It is known in the art to use a laser instead of a solder tip to reflow solder. Use of a laser avoids some of the disadvantages of the solder tip reflow process, and the laser can be focused to provide heat only to the desired area. Using a laser for reflow, however, has its own disadvantages. For example, one problem is regulating the heat being absorbed into the solder joint in order to obtain the correct temperature desired for reflow. Previously the laser beam has been aimed directly on top of the solder pad, as depicted in FIG. 1. FIG. 1 is a block diagram of a plan view of a solder joint assembly 10 as known in the art. The solder joint assembly 10 includes a substrate 11 on which is disposed the optical component 12. The output beam 16 of a laser 17 is positioned above a solder pad 14 and solder (not shown) in order to heat the solder.
One problem with placing the laser output 16 directly over solder pad 14 is that the solder has a surface finish that varies over part of the solder joint. This variation in the surface finish creates variability in the amount of energy that is reflected off the surface instead of being absorbed by the solder. The amount of heat that is reflected may vary widely from solder joint to solder joint, depending on the surface condition of the solder. For example, a solder joint may have flux remaining on it due to inefficient cleaning, which may affect the reflectivity of the solder. Additionally, absorption of energy by the solder is a function of temperature as well. The solder generally absorbs differently when it is hot than when it is at room temperature. Thus, the solder will heat unevenly unless its temperature is known when it is exposed to laser output 16. To correct this deficiency, an infrared (IR) detector may be used that provides temperature feedback; however this adds complexity to solder joint assembly 10. It is a challenge to measure temperature directly on the solder. Typically a very small spot size pyrometer is used to accomplish this, which adds further complexity and expense. Further, in certain situations there may not be enough room for the location of a temperature sensor.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
The present invention involves predictably heating a substrate rather than a metallic solder pad. The system and method for reflowing solder joints includes the use of a laser. A high-power laser beam can be focused to apply heat only to a specific area that is desired, and thus avoid all of the problems associated with using a solder tip. Further, the system and method of the present invention includes focusing the laser output on the substrate adjacent the solder pad, rather than directly on the solder itself. Because the substrate has a more consistent finish than solder, it absorbs energy much more uniformly and consistently than solder. By positioning the laser output on the substrate and heating the substrate rather than the solder pad directly, a more uniform and consistent reflow of the solder is accomplished. Thus, the present system and method can prevent cross-reflow as well as eliminate the need for a bulky, expensive, and/or complex temperature feedback system.
In the invention, the laser beam output may be located approximately 100 microns (xcexcm) from the edge of the solder pad. The laser beam spot size may be approximately 400 xcexcm. The laser power may be approximately six watts (W). For other applications, these parameters may be different.
Briefly described, one aspect of the system, among others, can be implemented as follows. A solder reflow system includes a substrate, a solder pad disposed upon the substrate, an optical component disposed upon the solder pad, and a laser positioned above the substrate with the laser output focused sufficiently close to the solder pad to reflow the solder when the laser is powered. The solder reflow system may include the laser output being positioned from approximately 100 to approximately 200 microns away from the solder pad. The substrate is heated by the laser output and transfers the heat to the solder.
The present invention can also be viewed as providing methods for reflowing solder. In this respect, the invention can include first providing an optical component assembly system. The optical component assembly may include a substrate, a solder pad disposed upon the substrate, solder disposed upon the solder pad, and the optical component also disposed upon the solder pad. The assembly system may also include a laser. The invention further includes positioning the laser output onto the substrate with its output focused sufficiently close to the solder pad but not directly over the solder pad. The laser is then powered so that energy is transferred through the substrate into the solder pad, reflowing the solder.
Clearly, not all of the above advantages listed herein will be present in every realization of the invention. Additionally, other systems, methods, features, and advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.